1. Field of the Invention
The present invention relates generally to a shaft assembly and in particular to a shaft assembly for a tilt adjustment mechanism for use in connection with a touch screen display tablet.
2. Related Applications
This application is related to co-pending application Ser. No. 08,436,941, entitled "Tilt Adjustment Mechanism" IBM Docket number RA9-95-026 hereby incorporated by reference.
This application is related to co-pending application Ser. No. 08/437,008, entitled "A Front Cover Assembly for a Touch Sensitive Device" IBM Docket number RA9-95-015 filed hereby incorporated by reference.
3. Description of the Prior Art
In order to provide for varying operator requirements and suitable glare resistance, touch displays must be rotated up and down within a certain range. This tilt adjustment helps compensate for operator height variations and ambient glare on the glass of the display surface. The touch display requires the use of touch for operator input so the tablet must withstand a touch force without moving. It is also desired that the touch display be adjustable with one hand without any releases or buttons. It is further desired that infinite adjustment be available within the range of motion. Since the touch display unit is not heavy, it is also desired to be able to adjust the tablet upward with one hand without lifting the unit off the counter.
There are several prior art techniques that solve some of the above requirements. One such technique is a hinge; however, a number of prior art hinges have various disadvantages. Some prior art hinges leave a large amount of free play before any resistance is felt by the user. Other hinges allow rotational movement of the members only in discrete steps through the use of a ratchet-type mechanism or a detent. Therefore, if the optimal viewing angle for a particular operator is between two discrete ratchet steps the operator much choose a position which is not optimal. A ratchet mechanism limits the adjustment to certain discreet points and would probably require release buttons. An unlock/adjust/lock mechanism could be employed but requires the use of release/lock buttons which can be difficult to maneuver with one hand. A friction device could be employed but is difficult to adjust upward without using one hand to pull upward and one hand to hold the system unit down. A friction device also provides the same resistance in the upward and downward directions. Another problem with these solutions is that the housing of the display tablet and system unit is plastic and flexible. Pushing or pulling on one comer of the tablet can cause the tablet to twist. This twisting action can cause the unit to adjust unevenly and cause damage to the tablet.